The role of cardiopulmonary receptors and baroreceptors in modulating salt and water excretion in the nonhuman primate during hypervolemia has not been well defined. The few studies which have been performed in the monkey have, however, indicated that blood volume control in this species may utilize different afferent neural pathways than those shown to be of major importance in the dog. The proposed studies will further explore neural modulation of renal excretion in the anesthetized monkey during two types of hypervolemic stimuli, outright volume expansion and head-out water immersion. Four projects are proposed as follows: (1) Determination of the necessity of dorsal spinal (C8 - T7), vagal and sinoaortic neural pathways for the renal responses to acute intravascular volume expansion. Monkeys in which these nerves have been severed will be volume-expanded with a cell-free solution and the time course and magnitude of the renal excretory and hemodynamic responses compared to sham-operated controls. A second portion of this project will examine the renal response to exchange dilution without volume expansion. (2) Role of vagal-aortic and carotid sinus nerves in modulating the renal responses to head-out water immersion. Monkeys will be immersed both in the intact state and after selective denervation of the aforementioned neural pathways and responses compared. (3) Role of cardiac nerves in modulating the renal responses to water immersion and volume expansion. Monkeys which have undergone chronic total cardiac denervation will first be immersed and then volume-expanded in the seated posture and their responses compared to sham-operated controls. If cardiac denervation fails to abolish the renal responses to both interventions, a second facet of this project will examine the responses after both cardiac denervation and vagotomy-sinoaortic denervation. (4) Role of renal nerves in the renal responses to water immersion and volume expansion. Monkeys will undergo chronic left renal denervation and be immersed and then volume-expanded. Utilizing separate ureteral urine collection, the renal responses of the denervated left kidney and innervated right kidney will be compared.